The invention relates to a positive-working radiation-sensitive composition. More particularly, the invention relates to a composition which is rendered soluble by irradiation, which comprises:
(a) a compound which forms a strong acid upon irradiation, PA1 (b) a compound having at least one acid-cleavable C--O--C bond, such as an acetal, and PA1 (c) a binder which is insoluble in water and soluble or swellable in organic solvents and in aqueous-alkaline solutions, PA1 R.sub.1 and R.sub.2 are identical or different and denote alkyl groups containing 1 to 6 carbon atoms.
and which is suitable for use in the production of radiation-sensitive recording materials such as photoresists, electronic components and printing plates and for chemical milling. Compositions containing the above-indicated components are described, for example, in U.S. Pat. No. 3,779,778, DE-A No. 27 18 254 (corresponding to U.S. Pat. No. 4,247,611), DE-A No. 29 28 636 (corresponding to U.S. Pat. No. 4,311,782), EP-A No. 0 006 626 (corresponding to U.S. Pat. No. 4,250,247) and in EP-A No. 0 042 562 (corresponding to U.S. Pat. No. 4,506,003).
Upon exposure of these materials, photolysis of compound (a) leads to the formation of acid which causes the cleavage of C--O--C bonds of compound (b) such that, as a result, the exposed areas of the light-sensitive layers are rendered soluble in the developer. These mixtures of substances are, however, not free from disadvantages.
The hitherto used polyacetals and polyorthoesters are in some cases not readily accessible and/or have the property of being obtained in various molecular weight distributions, depending on the conditions of condensation. This has an influence on both the production cost and the desired copying characteristics, in particular the constancy of light sensitivity of light-sensitive layers prepared from these compounds. The known light-sensitive compositions cannot contain more than a certain amount of acid-cleavable compounds; their main constituent comprises, as a rule, a binder which is insoluble in water and soluble in aqueous alkali, which gives the compositions an adequate overdevelopment resistance. However, this large amount of alkali-soluble binder, preferably phenolic resin, has the effect that layers formed from these compositions, in particular layers of relatively great thicknesses, are relatively brittle and tend to crack or splinter.
Up to now, it has been the prevailing opinion that for good imagewise differentiation the greatest possible number of cleavable C--O--C bonds, i.e. polymeric compounds, must be present, the C--O--C bonds being preferably in the main chain of the polymer, so that many small fragments which are considerably more soluble are formed from one polymer molecule.
DE-A No. 37 25 741 describes a radiation-sensitive composition which can contain as the acetal, inter alia, a compound of the general formula ##STR2##
It has now been found that, based on further available, industrially produced intermediate products, novel substituted malonaldehyde tetraacetals can be prepared, which are also well suitable for use in positive-working light-sensitive layers.